Gas detecting and analyzing methods and apparatus



Jan. 10, 1961 R. B. EDWARDS Erm.

GAS DETECTING AND ANALYZING METHODS AND APPARATUS Filed Jan. l5, 1957United States Patent() GAS DETECTING AND ANALYZING METHDS AND APPARATUSRobert Bruce Edwards, San Jose, Calif., and Ernest H.

Filed Jan. 15, 1957, Ser. No. 634,317

3 Claims. (Cl. Z50-41.9)

The present invention relates to improved gas detecting and analyzingmethods and apparatus. The methods and apparatus of the presentinvention are particularly well suited for the detection and analysis ofhydrocarbon gases present in the circulating fluid or mud used in thedrilling of wells which are indicative of the presence of petroleum ornatural gas, and for certain other gases, particularly hydrogen. Thesemethods and apparatus provide greater sensitivity and precision in thecontinuous logging of the gas content of the drilling mud as itrecirculates back to the surface of the earth from the bottom of a wellbeing drilled.

During the drilling of a well it is a customary practice to examine thedrilling fluid, or mud, to detect the presence of hydrocarbon gases andalso hydrogen and other gases. As the circulating mud passes the drill,it picks up cuttings from the drill. Successive elemental volumes of themud and the cuttings in these volumes retain traces of the hydrocarbongases present in successive strata through which the drill is passing atthe time. By analyzing the gas content of successive volumes of themud-cuttings mixture soon after they leave the mouth of the well and bycorrelating these gas content measurements with the successive depths ofthe drill from which they came, the geologists learn importantinformation on the characteristics of the underground formations throughwhich the drill passes.

The traces of hydrocarbons present in the mixture of mud and cuttingsare often very dilute so that extremely sensitive measurements must bemade to detect their presence. A great amount of time and effort hasbeen spent by many persons in eiorts to further this art of logging ofthe drilling mud.

The accompanying drawing is a schematic electrical circuit diagram ofimproved apparatus for detecting and measuring hydrocarbon gases,including automatic programming control mechanism for controlling thescanning of the various hydrocarbon gas constituents.

`One of the practices which has been adopted in the logging of drillingmud is the use of mass spectographs to detect and analyze thehydrocarbon gases liberated from the mixture of drilling mud andcuttings. In particular, linear-type electrostatic mass separators aretinding wide-spread acceptance. In these instruments, samples of thesegases are drawn into a highly evacuated chamber and are ionized bybombardment with a stream of electrons in a conventional type ionizationchamber. The ionized molecules of any gases present are then acceleratedout of the ionization chamber through -a set of electrostatic lenseswhich collimates the beam of ions. The ion beam then passes throughaligned apertures in a row of flat plates. Successive pla-tes along theline are spaced progressively farther apart, and the individual platesare energized by a radio frequency potential of predetermined frequency.Because ions of diiferent mass-to-charge ratios (m/ e) accelerate atdifferent rates, only ions of a certain selected mass-to-charge ratioremain in phase with the radio frequency potential for 2,967,932 YPatented Jan. l0, 1961 ICC any given frequency as they pass successiveplates and reach maximum velocity. At the end of the acceleration pathis positioned a dellector plate and a screen with a narrow slit therein.Only ions having the maximum velocity are properly detlected so yas topass through this slit. Thus, ions of the selected mass-to-charge ratioare separated from anyothers present. These selected ions form an ioncurrent which is then amplied and measured as an indication of theamount of .the correspending gas present. In order to measure theconcentrations present of ions of different weights, the radio frequencyapplied to the mass spectrometer is changed to different values. EachpredeterminedA frequencyvalue which is used corresponds to apredetermined selected ion mass. l

Expressing this in somewhat dilerent terms, each different sample of agas mixture obtained over a volume of `drilling mud contains severaldilerent gases. There are usually relatively heavy concentrations of theatmospheric gases such as nitrogen, oxygen, carbon dioxide, and watervapor. In addition, traces of one or more of the following hydrocarbongases and also hydrogen and other gases, may be present: hydrogen,methane, ethane, propane, butane, pentane, and hexane. When any one ofthese gases is present and is ionized, the apparatus gives a peakreading or peak value indication at a frequency setting correspondingwith the predetermined radio frequency which selectively acceleratesthese ions. This peak value indication is termed the mass peak for theparticular ionic mass under consideration.

Considering an atom of oxygen fas having a massof 16 units, these listedgases have the following mass values:

Gas Chemical Mass Formula Hydrogen H2 2 Meth'mn CH4 16 Ethan@ 02H5 3()Propane 03H5 44 Butane 04H10 58 Pentane 05H11 72 T-Toxann 06H14 86 tionsof approximately ten kseconds each. "Atathep end of each minute, theapparatus automatically begins repeating the sequence. l I j In thesemethods and apparatus provision is also made for repetitively measuringpaired combinations of mass peaks. The apparatus automatically switches"from measurement of one mass peak to the other [andback again. Eachmass peak .is measured for thirty' seconds, and at the end of eachminute, the cycle begins again.V

In addition, the apparatus described canhe set manually for continuousmeasurement, Le.' monitoring gof any one of six 'mass peaks. Wheneverdesired the apparatus may be immediately changed from monitoring onemass peak to another. v Y

Among the many advantages of' the methodsv andrapparatus of the presentinvention are those. resulting'from the fact that they enable sensitiveand accurate measurements to be made right atv the well 'site' whilehthedrilling continues. The automatic sequencingE fromoiie;

mass peak to another providesimportant analytical information concerningthe various gas constituents which are present. Continuous logging ofthe drilling mud is facilitated and'the magnitudes of the various masspeaks are analyzed in away which greatly helps the geologist inobtaining an early detection of underground petroleum and gas deposits.

The ratios of the concentrations of pairs of gas constituents which arepresent, and in particular between methane and the others, yieldsvaluable information concerning the petroleum and .gas content of theformations being drilled. The automatic switching between any one ofthese mass peaks and one of the other mass peaks provides a continuousmeasure of the ratio between the concentrations of the two gases beingmonitored and shows their concentrations in the gas sample.

In this specification and in the accompanying drawing, are described andshown embodiments of the improved gas detecting and analyzing methodsand apparatus of the present invention and various modifications thereofare indicated, but it is to be understood that these are not intended tobe exhaustive nor llimiting of the invention, but on the contrary aregiven for purposes of illustration in order that others skilled in theart may fully understand the invention and the manner of applyingtthemethod and apparatus in practical use so that they may modify and adaptit in various forms, each as may be best suited to the conditions of aparticular use.

The various objects, features, and advantages of the present inventionwill be more fully understood from a consideration of the followingdetailed description of methods and apparatus embodying the presentinvention in conjunction with the accompanying schematic circuit diagramof improved apparatus for detecting and measuring hydrocarbon gases.

In operation the circulating hydraulic fluid 1li after it issues fromthe mouth of a well being drilled is conveyed through channel means 11,shown as a pipe seen in cross section. Connected to the hydraulic fluidchannel is a gas sampling tube 12 feeding through a valve 14 to a massspectrometer 16 schematically represented in block form as beingalinear-type mass separator tube.

In order to select the desired mass peak, a radio frequency oscillator18 has its output coupled into the mass spectrometer 16. The radiofrequency potential is applied in opposite phase relationship toalternate plates along the ion path within the mass spectrometer bycoupling one of the oscillator output terminals 19 to alternate platesand by coupling the other terminal 20 to the intervening plates. One ofthese output terminals may be connected to the common return or groundcircuit of the apparatus as indicated by the ground symbol appearing atthe terminal 19.

A resonant circuit, generally'indicated at 22, controls the frequency ofthe oscillator. 'Ihis resonant circuit includes an inductance winding 24shunted by an adjustable capacitor 26. One side of the resonant circuitis connected by a lead 28 to the common return circuit and the otherside of this resonant circuit is connected by a lead 30 to asix-position switch 32. This switch is arranged electivcly to couple anyselected one of six adjustable capacitors 34, 35, 36, 37, 38., and 39between the leads 28 and 30, thus tuning the frequency of the oscillator18 to any one `of six .selected mass peaks, `'as may be desired by theoperator. This switch 32 is driven by means of a mechanical linkageschematically indicated at 40 driven by a rotary stepping solenoid 42.The operation of this rotary stepping solenoid is explained in detailfurther below.

For the purpose of eliminating spurious responses in the amplifiercircuits and to enable easier amplification, a modulator 44 feeds analternating voltage into the mass separator tube. This modulator appliesan .alternating voltage of a distinctive frequency to a grid circuitarranged to modulate the ion beam in the tube. The modulator frequencyis a convenient value of relatively low frequency compared with theoscillator 18 and is distinctively different from 60 cycles or aharmonic thereof. For example cycles per second may be used toadvantage.

The resultant modulated beam of ions of selected mass produces analternating voltage signal which is initially amplified in apre-amplifier 46. The signal is then fed through a pre-set attenuatorcircuit 48 and through a main amplifier circuit S0 to a synchronousdemodulator 52 which is also under the control of the modulator 44 asindicated schematically by the connection 54. From the demodulator aunidirectional current signal is fed by means of a pair of connections55 and 56 to a recording pen mechanism in a chart recording instrument58. Thus, the recorder plots values as a function of the magnitudes ofthe mass peaks being measured.

In order to calibrate the apparatus to yield recorded values asfunctions of the quantities of the various hydrocarbon gases present,samples of known mixtures of gases are fed into the mass separator tube.The pre-set attenuator 48 is then set to produce the desired reading atthe recorder for each mass peak.

In certain instances it is desirable to provide for suppression of thebackground of each mass peak. This function is obtained by a zerosuppression circuit schematically indicated in block form at 60. Thiszero suppression circuit feeds a predetermined fraction of the modulatorvoltage into the pre-amplifier 46 so as to prevent the recorder fromgiving any indication when the values of the individual mass peaks fallbelow the respective zero suppression levels chosen for them.

In order automatically to control the operation of the apparatus, anautomatic peak programming circuit is utilized, as indicated at 62 inthe center of the drawing. This peak programming control circuit can beadjusted readily for any one of three modes of operation by means of amanually operable ganged tive-position switch 63 having six contact arms64, 65, 66, 67, 68 and 69. When this switch is in its extreme left-hand,or counterclockwise position, the peak programming control circuit isadjusted for continuous scanning or monitoring of any one of six masspeaks. The particular mass peak desired for monitoring is selectedmanually by turning a manual selector switch 70 including first andsecond ganged sections, 71 and 72, respectively, into any one of sixpositions. This left-hand position of the switch 63 is called the manualposition.

The switch 63 can be turned through a stop position at which noindications are recorded to a center position called the pairs position.When the switch 63 is in the pairs position, a second mode of operationis produced. The apparatus automatically repetitively scans one masspeak for thirty seconds and then scans any one of live other desiredmass peaks for thirty seconds. Under most conditions, for typicaldrilling operations it is found most advantageous to include methane asone of the pairs of mass peaks being monitored as giving the mostsensitive indication. But occasionally one of the other light gases suchas hydrogen, ethane, or propane may be used to advantage in these pairedcombinations, for example, when the drilling is approaching a formationin which the ratio between one of these other light mass peaks andanother particular mass peak is expected to show a marked variation fromthe average. The other mass peak to be scanned in a paired combinationwith one of these light mass peaks is determined by the operator byturning the manual selector switch 70 to the desired position.

By turning the-switch 63 further to the right, it passes througlrasecond stop position and then reaches the sequence position producingautomatic repetitive sequencing of the apparatus through any desired sixmass peaks, dwelling 1() seconds on each.

In order to control the position of the rotary stepping solenoid 42, anautomatic selector switch, generally indicated at 80 is coupled to thesolenoid by means of the drive linkage 40. This switch 80 includes twosections 81 and 82, which are respectively identical with the sections71 and 72 of the manual selector switch 70. When set for scanning of apair of mass peaks, for example, including methane and one of the otherhydrocarbons listed above, the selector switch 80 is automaticallypositioned by the stepping solenoid 42 in accordance with the setting ofthe manual selector switch 70` during alternate 30-second periods.During the intervening 30-second intervals, the sequencing control 62automatically scans the methane mass peak, as will be explained furtherbelow.

For signalling the mass peak being scanned, a sixposition signal lightcontrol switch 84 has a rotating contact arm 86 connected by a lead 87to one side of a low voltage source, shown as a 6.3 volt alternatingcurrent source. Six signal lamps 88, 89, 90, 91, 92, and 93 areconnected to respective individual contacts of the switch 84 and are allconnected through a lead 94 to the other side of this low voltagesource.

For recording a steady mark on the record chart in the recorder 58, asan indication of which mass peak is be ing scanned, a direct currentsignal of fixed value is produced by a function marker control switch96. This switch 96 is a six-position switch and has a contact arm 98also driven by the linkage 40 in synchronism with the other switches 86,80, and32.

The six contacts of the switch 96 are connected to six spaced pointsalong a resistance potential divider 100 which has a direct voltagedeveloped across it by a rectifier 102 and a filter circuit 104energized from the leads 87 and 94. As the contact arm 98 is positionedon successive contacts in the switch 96, a successively different steadyvoltage is fed through a pair of leads 105 and 106 to a functionindicating pen drive mechanism in the recorder 58. Thisproduces acontinuous recorded, mark which steps from one fixed value to another asdifferent mass peaks are scanned. v

Automatic sequence scanning method and operation y For purposes ofexplanation of the operation of the peak program control 62, assume thatthe switch 63 is turned to the sequence position, A synchronous typemotor 110 geared to produce an output shaft speed of l revolution perminute is energized with 115 Volt, 60 cycle current from a pair of mains111 and 112. The motor energizing circuit is traced from the main 111through a line 113 and a fuse 114 and a lead 115 to one terminal of themotor 110. The return from the other terminal of the motor passes alongleads 116 and 117 and through the right contact 118 to the switch arm 69and back through the line 119 to the main 112. The motor turns five cams120, 121, 122, 123, and 124, respectively operating five single-polemicro-switches 125, 126, 127, 128,` and 129. The first four of theseswitches 12S-128 are double-throw switches, and the associated cams1Z0-123 are arranged to move their contact arms in synchronism back andforth, dwelling in each closed position for 30 seconds.

The fifth micro-switch 129 is a single-throw switch and its operatingcam 124 has six raised areas arranged to swing the contact arm 130 tothe left, or closed position six times each minute, holding the switch129 closed for approximately seconds upon each closure. This switch arm130 completes a circuit from a junction point 131 between a capacitor132 and a rectifier 133 to a sequence control bus 134 connected to theright or sequence contacts 135, 136, 137, and 138, of the first foursections of the manual switch 63.

With the switch 63 inthe sequence position, as assumed above, the switcharms 64, 65, 66, and 67 engagethe contacts 135, 136, 137, and 138,respectively, thus connecting the bus 134 to each of four control linesA,,B, C, and D, respectively. These control lines run to four contactsa-l, b-l, c-l, and d-1 of the switch section 81, respectively, and alsoto four contacts e142, b-2, c-,2, and d-2 of the switch section 82.Dependingdupon the position of the rotatable switch disk of theswitch82, one or more of the control lines A, B, C,V and D are connectedto aswitch contact 141. A resistor 142 in series with a capacitor 143 isconnected from the contact 141 to the power line 119, and the controllines A, B, C, and D are connected by the contact 141 to a Wire 144running to one terminal of the rotary stepping solenoid 42. A wire 145runs from the other terminal of this solenoid to the sequence (right)contact 146 of the fth section of switch 63.

`When the manual switch arm 69 engages the contact 118, it alsocompletes a circuit from one A.C. power line 119 through the lead 116and the rectifier 133 and capacitor 132 in series to the other A.C.power line 113,

to turn the linkage 40 to the next sequential position.

where it remains for 10 seconds, thus scanning one of the mass peaks forthis period of time.

When the cam-actuated switch 129 momentarily opens at the end of thefirst 10-second period, the capacitor 132 recharges. Upon the nextclosure of the switch 129, this capacitor again discharges, advancing tothe next mass peak for a 10-second scanning period. In this way anautomatic cycle of" one minute duration is obtained, repetitivelyscanning in sequence six mass peaks for equal periods of approximately10 seconds each.

The particular mass peaks chosen are predetermined by adjustment of thevarious tuning capacitors 26, 34, 35, 36, 37, 38, and 39 controlling thefrequency of the osci'lator. It is usually most desirable to select asmass peaks those representative of six of the seven following gases:hydrogen, methane, ethanepropane, butano, pentane, and hexane. Theparticular mass peaks which are usually found most useful do not allcorrespond exactly with the relative molecular weights as listed above,for the following reasons.

During the ionization of the various hydrocarbon gas molecules some ofthem are broken up or fractionated to a greater or lesser degree underthe impact of the ionizing beam of electrons. The result is afractionation pattern involving several mass peaks for each type ofmolecule.

Because yof the relatively large numbers of molecules of each typeinvolved, the fractionation pattern ofv mass peaks for each type ofmolecule is a fixed pattern, resulting from statistical averaging overlarge numbers.

Many of the mass peaks resulting from the fractionation i of the heaviermolecules. for example, such as pentane and hexane coincide with theprincipal mass peaks of the lighter molecules.

butions to the lighter mass peaks by the fractionation patterns of thevarious heavier molecules. The fractionation pattern'of any given typeof molecule is calibrated Thus, in reading the relative values of thesix mass peaks allowance is made for the contrif tern and use mass peak15 instead. This mass peak.. l5 results from ionizing collisions ofmethane molecules in which one or the four hydrogen atoms is knockedoff, and it is the largest side mass peak (i.e. other than the principalone at mass 16 for methane under usual operating conditions.

Because of coincidence with mass peaks in the fractionation patterns ofheavier molecules, it is usually desirable to avoid mass peak 44 for ameasure of the propane concentration. Instead, the use of`mass peak 42is usually a more sensitive and accurate indication of propaneconcentration.

In summary of the sequence operation, the apparatus automatically scansany six desired mass peaks in repetitive cycles of seconds each. Themass peaks of 2, 15, 30, 42, 58, 72, and 86 are particularly useful forindicating respective ones of the eight listed gases. At the end of eachminute the cycle automatically begins again. At the same time, thesignal lamps indicate at a glance which mass peak is being scanned, andthe function pen records a xed value indication on the recorder chartshowing which mass peak is being scanned.

Automatic pairs scanning method and operation For automatic pairsscanning, the manual control switch 63 is turned to its center position.The motor 110 is now energized through the switch arm 69 and the centeror pairs contact 148. Also, the other terminal of the solenoid 42 is nowconnected through a rectitier 150 and ,a lead 152 to the pairs or centercontact of the fth section of the switch 63, which is engaged by the arm68 and thus completes a circuit to the power line 113.

Directing attention to the first four sections of the manual controlswitch 63, it is seen that the contact arms 64, 65,66, and 67,respectively, when in the pairs position complete circuits from thecontrol lines A, B, C, and D to the switch arms 155, 156, 157, and 158of the iirst four cam-actuated switches 125, 126, 127, and 128,respectively. The four associated cams 120, 121, 122, and 123,respectively, swing these switch arms into engagement with the rightcontacts for approximately 30 seconds during each minute of operationand into engageinent with the left contacts for the remaining 30 secondsduring each minute.

When the four switch arms 155, 156, 157, and 158 are swung to the right,the three control lines A, B, and C are connected to a bus 159 runningto the lead 116 and thus are coupled to the power line 119. However, thecontrol line D is left unconnected from the bus 159, for the rightcontact 154 of the switch 128 is unconnected.

In eiect then, the control lines A, B, and C are energized with voltagefrom the A.C. power line 119. Thus, whenever the switch disk 146 engages`any one of the contacts a-2, b2 or c-2, a circuit is completed from thepower main V112 through the solenoid 42 and through the .rectifier 150to the switch arm 68 and thus back through the fuse 114 to the otherpower line 113. This energizes the solenoid causing it immediately toturn to the next position. The switch disk 140 has three contact lugs x,y, and z and three depressions therebetween. The lug is wide enough toengage only one of thercontacts a-Z, b-2, c2 or d-2. Thedepressionbetween lugs x and y is wide enough simultaneously to Iavoidtwo of these contacts. The lug y is wide enough simultaneously to engagetwo of these contacts, while the depression between lugs y and z willonly avoid one of these contacts. The lug z is wide enoughsimultaneously to engage three of these contacts, and the depressionbetween lugs "z" and x is wide enough simultaneously to avoid three ofthese contacts.

By virtue of this shape of the cont-act disk 146, the solenoid 42 isenergized and turns quickly from position to position until the lug "xengages the dead contact d-.Z and the adjacent'widest depression avoids,all three 8 of theenergized contacts a2, b-2, and c-2. In this positionthe rotary stepping solenoid 42 is de-energized and ceases turning.

Thus, Vthe oscillator 18 is automatically tuned to a preselected masspeak. usually one of the lighter mass peaks, for example, such as themethane mass peak 15, and the scanning of the methane mass peakcontinues for approximately 30 seconds. Then, during the next 30 secondperiod, `the four cams 120, 121, 122, and 123 move the switches 125,126, 127, and 128 to their left positions, connecting the control linesA, B, C, and D., respectively, to four control lines E, F, G, and Hwhich run to the contacts e4, f-1, g-1, and h-1 and e-Z, f-2, g-2, andh-Z of the manual selector switch 70. The contact disk 160 of the switchsection 72 has three lugs w, v, u, yand is identical in configurationwith the switch disk 140. The lug "w is wide enough to engage only onecontact; the lug "v is wide enough to engage two contactssimultaneously, and the lug u is wide enough to engage three contactssimultaneously. A longer contact 161 always cngages the disk 160 and isconnected by va lead 162 with the power line 119. Thus, depending uponthe angular posi tion of the manual selector switch 70, one or more ofthe control lines E, F, G, or H and consequently one or more of thecorresponding control lines A, B, C, and D are energized from the powerline 119.

The rotary stepping solenoid 42 is correspondingly energized and movesaround to a position in which the lug "x is Iat an angular positioncorresponding with the angular position of the depression between thelugs "u" and "v of the contact disk 160. In other words, the solenoid 42is energized until depressed areas in the disk are opposite whicheverones of the contacts a-2, b-2, c-2, and d-2 are being energized from thecontact 161 as a result of the angular position of the switch 70.

In effect then, the solenoid 42 and switch 80 are made slave to theposition of the manual selector switch 70 during the alternate 30-secondintervals when the four cam-actuated switches 125, 126, 127, and 128interconnect the control lines A, B, C, and D respectively, with thecontrol lines E, F, G, and H.

In this way an automatic scanning of the methane mass peak l5 in pairedcombination with any one of the other mass peaks is obtained, the manualcontrol switch 7 0 being turned to select whichever one of the othermass peaks is desired. Usually the methane and ethane mass peaks areused as a paired combination because they yield the most sensitiveindications of the presence of petroleum or gas.

Manual operation By turning the control switch 63 to its left or manualposition the motor 110 is de-energized. The lead 152 from the rectier isagain connected to the power line113 by means of the switch arm 68. Atthe same time, the four switch arms 64, 65, 66, and 67 directly connectthe control lines A, B, C, and D respectively to the control lines E, F,G, and H. This makes the automatic selector switch 70 and solenoid 42continuously opcrate in slave relationship to the angular position ofthe manual selector switch. Whenever the operator turns the manualselector switch to select a different mass peak, the solenoidimmediately turns the linkage 40 to the proper position for scanning ofthe selected mass peak.

11n order to tune the zero suppressor 60 and pre-set attenuator 48 tovarious 'values corresponding with the desired calibration of theapparatus, another pair of switches identical with the switch 70 mayalso be driven by the linkage 40. Then an automatic selector switch anda rotary stepping solenoid such as the switch 70 and the solenoid 42 areincluded in the suppressor circuit and in the attenuator circuit. Thus,the tuning of the suppressor and attenuator is made automatically tofollow the tuning of the selector switch 80.

From the foregoing it will be understood that the improved gas detecting'and analyzing methods and apparatus of the present invention describedabove are well suited to provide the advantages set forth, and sincemany possible embodiments may be made of the various features of thisinvention and as the method and apparatus herein described may be variedin various parts, all without departing from the scope of the invention,it is to be understood that all matter hereinbefore set forth or shownin the accompanying drawing is to be interpreted as illustrative and notin a limiting sense and that in certain instances, some of the featuresof the invention may be used without a corresponding use of otherfeatures, all without departing from the scope of the invention.

What is claimed is:

l. Apparatus for logging the hydrocarbon gas content of mixtures ofunknown gases comprising measuring means having a plurality of differentoperating conditions and selectively measuring the relativeconcentrations of the following six hydrocarbon gases: methane, ethane,propane, butane, pentane, and hexane, each operating conditioncorresponding with the measurement of one of said gases; tirs-t switchmeans connected to said measuring means and having six positions eachone corresponding with and producing one of said measurements; secondswitch means having a pair of positions, one of said pair correspondingwith measurement of methane, and the other of said pair interconnectingsaid second and first switch means and producing a measurementcontrolled by said first switch means; and cyclic drive means operatingsaid second'switch means back and forth between said pair of positions.

2. Apparatus for logging the hydrocarbon gas content of mixtures ofunknown gases comprising ionizing means; measuring means having aplurality of different operating conditions and selectively measuringthe relative concentrations of ions of masses 15, 30, 42, 58, 72, and86, each operating condition corresponding with and controlling themeasurement of a selected one of said ion masses; first programmingswitch means connected to said measuring means and having six positionseach one producing a selected one of said measurements; secondprogramming switch means connected to said measuring means and having atleast two operating positions, one of said latter positions producingthe measurement of ion mass 15 and another of said latter positionsinterconnecting said second and first switch means and producing ameasurement of an ion mass selected by said first switch means; andcyclic drive means operating said second switch means repetitively fromone to another of said latter positions.

3. Apparatus for logging the gas content in drilling mud comprising gasconducting means for withdrawing a gaseous mixture including gasconstituents from the mud, ionizing means for ionizing said gaseousmixture, radio frequency mass selecting oscillator circuit includingfrequency con-trolling elements and having a plurality of dierentoperating frequencies as controlled by said frequency controllingelements, each frequency indicat ing the relative concentration of aparticular gas in said mixture, iirst and second switching mechanisms, amanual selector control connected to said switching mechanisms forselectively placing said tirst and second switching mechanisms inoperation, and a motor drive connected to said rst and second switchingmechanisms and under the control thereof, said motor drive being coupledto said frequency controlling elements and when said iirst switchingmechanism is operative cyclically switching between two frequencies,dwelling at each frequency for predetermined lengths of time, and whensaid second switching mechanism is operative sequentially switching toeach of said different operating frequencies, dwelling at each frequencyfor the same period of time.

References Cited in the file of this patent UNlTED STATES PATENTS2,508,163 nipple May 16, o 2,798,956 Lanneau et al. July 9, 19572,857,251 Krogh Oct. 2l, 1958

